1. Field of the Invention
The present invention relates to a protection circuit board, a battery pack including the protection circuit board and a method of fabricating the protection circuit board, and more particularly, the present invention relates to a protection circuit board which can realize a compact battery pack and a higher capacity than a conventional battery pack having the same size by changing electrical connections between a bare cell and a protection circuit board, a battery pack including the protection circuit board and a method of fabricating the protection circuit board.
2. Description of the Related Art
In recent times, various compact handheld electronic/electrical devices, such as cellular phones, notebook computers, camcorders, and so on, have been widely developed and produced. The handheld electronic/electrical devices include a battery pack installed therein to operate the devices without a separate power source. Battery packs may be classified into nickel-cadmium (Ni—Cd) batteries, nickel-metal hydride (Ni-MH) batteries, and lithium (Li) batteries. A battery pack using a secondary (rechargeable) battery is generally used in consideration of economic efficiency.
Among the types of batteries, the lithium ion secondary battery is widely used for the handheld electronic/electrical devices due to an operating voltage three times higher and a higher energy density per unit weight than the Ni—Cd battery and the Ni-MH battery. Lithium ion secondary batteries may be classified into Li ion batteries using a liquid electrolyte and Li polymer batteries using a polymer electrolyte depending on the kind of electrolytes, or may be classified into a cylindrical, rectangular or pouch type batteries, depending on the shape thereof.
Generally, a battery pack includes a bare cell which can be charged or discharged, and a protection circuit board electrically connected to the bare cell.
The bare cell is formed by accommodating an electrode assembly including a positive electrode plate, a negative electrode plate and a separator disposed therebetween, and an electrolyte in a can, and sealing the can with a cap assembly including an electrode terminal electrically connected to either the positive electrode plate or the negative electrode plate.
The positive or negative electrode plate which is not electrically connected to the electrode terminal is electrically connected to a cap plate of the cap assembly or to the can, which thus serves as a terminal, and the electrode terminal is electrically insulated from the cap plate and the can.
The protection circuit board is electrically connected to the electrode terminal of the bare cell, and to the cap plate or the can, thereby controlling voltage or current during charging/discharging of the bare cell to prevent an overvoltage or overcurrent in the bare cell.
The battery pack is fabricated by arranging an electrode assembly into an opening on one side the can. The electrode assembly includes a positive electrode plate and a negative electrode plate formed by applying a positive electrode active material and a negative electrode active material to a positive electrode collector and a negative electrode collector and a separator formed between the positive electrode plate and the negative electrode plate and then stacking and winding them.
Then, a cap assembly is attached to the open side of the can, an electrolyte is injected into the can through an electrolyte injection hole of the cap assembly, and the electrolyte injection hole is sealed, thus completing the bare cell.
Subsequently, a first lead plate and a second lead plate respectively electrically connected to an electrode terminal and a cap plate or a can of the bare cell, are electrically connected to third and fourth lead plates, which are electrically connected to the protection circuit board, and a space formed due to the electrical connection between the first to fourth lead plates is filled using resin, thereby preventing an occurrence of an electrical short-circuit between the bare cell and the protection circuit board, thus completing the battery pack.
To electrically connect a bare cell to a protection circuit board, in the conventional battery pack, first and second lead plates electrically connected to the bare cell were electrically connected to third and fourth lead plates electrically connected to the protection circuit board using a soldering process or a welding process, such as resistance welding. Also, a specific-sized space should be maintained between the bare cell and the protection circuit board for smooth welding. Thus, the space between the bare cell and the protection circuit board could not be smaller than a predetermined amount.
Also, in order to prevent an occurrence of electrical short-circuits due to moving of the bare cell and the protection circuit board, the space between the bare cell and the protection circuit board is filled in. However, defects may occur in the filling process, or the bare cell or the protection circuit board may be misplaced, thereby making electrical connection therebetween unstable.